Finned tube



April 8, 1947. J. w. BROWN, JR

FINNED TUBE Filed Aug. 11, 1943 INVENTOR. Joly/V w- .BIPOWM ave.

Patented Apr. 8, 1947 FINNED TUBE John W. Brown, Jr., Lakewood, Ohio,assig'nor to Brown Fintube Company, Elyria, Ohio, a corporation of OhioApplication August 11, 1943, Serial No. 498,199

Claims. (CL 257-262) This invention relates to heat exchange elementsand more particularly to finned tubes and methods of making same.

A general object of the invention is the .pro-

vision of a heat exchange element provided with a plurality ofseparately formed fin members extending generally transversely of theelement and welded thereto, the arrangement being such that the weldingoperation can be carried out rapidly and economically to provideadequate paths for the flow of heat between the fin members and thetube. Another object is to provide an efiicient and economical method ofmaking such heat exchange elements. More specifically an object of theinvention is to provide a finned tube having circumferentially extendingfin members secured thereto, the fin members being constructed andarranged so that they can be welded to the tube rapidly and economicallyto provide adequate paths for the fiow of heat between the fin membersand the tube. Another object is to provide a method of making suchfinned tubes. A further object is to provide heat exchange elements, andmore specifically, finned tubes, wherein the heat exchange surface isaugmented by fin members extending both transversely and longitudinallyof the elements or tubes. A further object is to provide a tube of thistype which has much greater strength to resist lateral deflection" thana base tube of the same size, gage and material. Another object is toprovide efficient and economical methods of making such ele ments ortubes. Further objects and various advantages of my invention willbecome apparent from the following description of preferred formsthereof, reference being made to the accompanying drawings. Theessential characteristics are summarized in the claims.

My invention is useful in conjunction with tubular or other surfaces,wherein it is desired to augment the effective heat transfer area. Theinvention is described herein as applied to finned tubes, and apreferred form of the invention may comprise a tube in which effectiveheat transfer area is augmented by a plurality of fin members secured tothe exterior of the tube and extending in generally transverse orcircumferential directions. Each fin member comprises a base portionadapted closely to engage the tube, and a plurality of finned portionsextending outwardly from the base portions. The fin portions are spacedapart while the base portions preferably bridge the spaces between thefin portions. The

various fin members are arranged on the tube so that the spaces arealigned to provide, along the exterior of the tube, unobstructed,longitudinally extending paths such that a resistance welding electrode,such as a roller electrode, can be moved along the paths, making contactsuccessively with the base portions of a series of fins, and thuswelding the transverse fins to the tube by welding operations in whichthe relative movement between electrode and tube is longitudinal of thetube, i. e., transverse to the fins. By this arrangement a series offinned members can be welded to the surface of the tube by operationswhich can be carried out continuously for the length of the finnedportion of the tube and at high speed. In the case of tubes, at least apair, and preferably two or more pairs, of diametrically opposite pathsare provided, and the welding operation is carried out by oppositelydisposed electrodes engaging the base portions of the series of finmembers and arranged simultaneously to weld oppositely disposed areas ofthe bases of the fin members to the tube.

According to another form of my invention, longitudinally extendingchannel section fin members may be disposed in the paths formed by thespaces or slots and welded to the base portions of the transverse finmembers by the same operation that is employed to weld the base portionsto the tube. These channel section members may be left in channelsection form may have their flanges bent inwardly and preferably weldedtogether as described in my co-pending application, Serial No. 386,503,filed April 2, 1941, now Patent No. 2,355,621, issued August 15, 1944.The various welding operations may be carried out by an apparatusgenerally similar to that disclosed in my Patent No. 2,298,249, issuedOctober 6, 1942.

Referring to the drawings which illustrate finned tubes made accordingto preferred forms of my invention, Figure 1 is an end view of a finnedtube embodying my invention and showing the welding electrodes inpositioii for carrying out the welding operations; Figure 2 is alongitudinal view partially in section of the tube shown in Figure 1;Figure 3 is a perspective View illustrating a portion of the tube ofFigures 1 and 2; Figure 4 illustrates modified forms of fin memberswhich may be employed in tubes made according to my invention; Figure 5is an end view showing a modified form of tube and diagrammaticallyillustratlng the welding operation; Figure 6 is an elevation of the tubeshown in Figure 5 as indicated by the line 6-45 of Figure 5; and Figure'7 is an end elevation of a tube such as that shownin Figures 5 and 6and in which the longitudinally extending channel section members havebeen closed to provide a somewhat streamlined shape.

Referring particularly to Figures 1, 2 and 3, a finned tube madeaccording to a preferred form of my invention may comprise a tube lhaving a plurality of fin members indicated generally at ll securedthereto. The fin members are preferably comparatively light gauge metalstampings, each having a plurality of fin portions indicated at l2, l3,I4 and i5 and generally cylindrical hub or base portions l5 adaptedclosely to engage the outer surface of the tube.

In order to make it possible for the fin members to be rapidly andeconomically welded to the tube, the several fin portions of each finmember are spaced apart as indicated at l1, l8, I9 and 20, the spacesextending inwardly to the hub or base portions. Thus when a plurality offin members are assembled on a tube with the spaces aligned,substantially unobstructed longitudinally extending paths are providedthrough the aligned spaces and along the outer surfaces of the base orhub portion I8. Preferably the paths are straight and parallel to theaxis of the tube. However, for some purposes it may be desirable toprovide paths which are somewhat curved, for

' example, steep spiral paths extending along and around the tube. Thealignment of the spaces needs only to be suflicient to permitunobstructed movement of the electrodes along the paths.

It will be noted that the several fin members preferably are assembledin such manner that the hub portions are in contact with each other, andthe fin members preferably are constructed so that the ends of the hubportions between the fin portions are substantially flush with the finportions at their juncture with the base portions as shown at 22 inFigure 2. Thus when the fin members are assembled on the tube there areno substantial gaps between the base portions of adjacent fin members,thereby providing a substantially smooth surface along the assembledbase portions through the longitudinally extending paths.

With an arrangement of this sort, the fin members can be resistancewelded rapidly and economically to the supporting tube structure bycurrent supplied through a pair of oppositely disposed electrodes,preferably rollers as indicated at 23 and 24 in Figure 1. By applyingsuitable welding pressure and causing a suitable welding current to flowbetween the electrodes while moving the tube and fin assemblylongitudinally with respect to the electrodes, diametrically oppositeareas of the bases of the whole series of fin memers can be welded tothe tube by a single continuous operation. After one series of op sitelydisposed welds has been made, the tube may be indexed so that theelectrodes will pass along another pair of paths, such as the pathsprovided by the spaces i8 and 20, and the welding operation repeated toprovide two more rows or series of welded areas 25. In the drawing Ihave illustrated only two pairs of paths and two pairs of series ofwelds. Those skilled in the art will appreciate that additional pairs ofpaths and welds may be provided if desired.

The welding operation is preferably carried out generally according tothe disclosures of my prior patent and application-aforesaid, thewelding current being controlled by means of an electronic control toprovide a series of substantially evenly spaced welded areas. Thewelding operation is preferably carried out at a sufficiently high speedso that the metal of the tube does not become excessively heated and isnot unduly softened. Thus the tube is enabled to withstand the weldingpressures without requiring the use of any internal mandrel. As anexample of a procedure which gives satisfactory results, I refer to thefollowing:

Fin members stamped from low-carbon steel, 0.035 inch in thickness,having base portions about 1 inch in internal diameter and about A inchin axial length (giving 4 fin members per inch of tube length) and withfour radially extending fin portions spaced about 5 inch apartcircumferentially at the juncture of the fin portions with the base orhub were welded on a 1 inch 0. D., 12 gage low-carbon steel tube, usinga k. v. a. welding machine with Thyratron control of the weldingcurrent. Diametricaliy opposite welding rolls with a width of 36; inchengaged the bases of the fin members in opposite paths and currentapplied simultaneously to produce two diametrically opposite rows ofevenly spaced welded areas extending substantially throughout the lengthof the assembled fin bases. the welding current fiowing through the tubewalls between the welds, no internal mandrel or electrode beingemployed. The welding pressure exerted by the electrodes was about 800to 1000 pounds, the speed oi movement of the tube and fins relative tohe welding axis was about 10 feet per minute. The 60 cycle alternatingcurrent was controlled by the electronic control to give a timing of 2cycles on and 4 cycles 01!, giving about five slightly overlappingoval-shaped welded spots per inch of tube. thus producing welded areashaving scalloped edges as shown in the drawing. The current was about40% of rated capacity of the machine at 6 to 8 volts. This gives aneflective heating current equivalent to about 9600 amperes flowing for 2cycles.

By varying the number of slots or paths in the fins and by varying thelength of the hub or base portions, the area of the welds between thetube and the base portions can be varied so as to give ample heattransfer capacity for the surface for which the tube is designed. Thelimiting factor in the transfer of heat from the hub or base to theseveral fin portions is the cross-sectional area of the fin portions attheir connection with the base portions. By proper spacing andproportioning, the welded areas can be made of such size that they willgive paths for the transfer of heat from the tube into the base and tothe junctures of the fins with the base at least substantially equal tothe total crosssectional area of the fins at their Junctures with therespective base portions. ample given above, the cross-sectional area ofeach fin portion at its juncture with the base portion is about 0.0185square inch, while the welded area between each pair of fin members isbetween 0.020 and 0.030 square inch depending on the extent of thescallops, the welded area being a little less than /o4 inch in width andextending throughout the axial length of the hub or base portion. Thearea is cut down as compared to a weld with straight edges by thescalloped edge effect, but the perimetric length is increased. Thelength of the juncture between each fin portion and the base along thecircumference of the tube is about 0.53 inch, the total for the fourfins being about 2.14 inches. The length of the edges of each weld onthe base. disregarding the ends of the welds where the welds areinterrupted by the Joints between suc- Thus in the excessive baseportions, is about the same as the circumferential length of each baseportion, due to the increase in length of the edges as compared to theaxial length of the bases because of the scallop effect, thus providingadequate paths for the fiow of heat from the welded spots into the base.Obviously, by employing base portions of greater axial length, by usingwider electrodes, or by other changes in proportions, the area andperimetric or edge length of the welds may be varied to give therequired paths for efficient heat transfer. For example, where heaviergage fins are used, it may be desirable to obtain additional heatconductive capacity between tube and fins by providing additional rowsof welds.

In the example given, the timing of the current and the speed ofmovement are such as to give about five welds per inch, whereas thereare four fin members per inch. Thus the welding electrodes will at timesroll over joints be tween adjacent base portions while the weldingcurrent is flowing. This presents no diificulty,

for the bases are closely spaced and the path over the joints is quitesmooth. However, if

desired, the timing of the current may be correlated with the speed ofmovement and the number of fin members per unit of length so the Vcurrent will be interrupted as the electrodes pass over the Jointsbetween adjacent base portions. This technique, while not essential,will somewhat reduce the wear on the electrodes.

Tubes of this character are particularly adapted for use in heatexchangers where the flow of fiuid on the exterior of the tubes istransverse of the axis of the tubes. While the flow of fluid acrosstubes such as shown in Figures 1, 2 and 3 will ordinarily besufilciently turbulent to meet the requirements of most installations,for some services it may be desirable further to increase the turbulenceof flow of fluid on the exterior of the tubes. In Figure 4, two modifiedforms of fins are shown which will have this effect. In this figure,only one fin of each type is illustrated. However, in actual use, aseries of fin members arranged as shown in Figures 2 and 3 wouldordinarily be employed.

The fin member 21 shown in the left-hand portion of Figure 4 has a hubportion 28 similar to the hub portion [6 heretofore described andsecured by welds 29 which may be similar to the welds 25 heretoforedescribed. In this instance, however, there are 8 separate fin portions30, and 8 spaces 3| between the fin portions providing 8 paths for theelectrodes so that each base portion may be secured to the tube by 8circumferentially spaced welded areas. Further. each fin portion istwisted slightly as shown in the drawing to increase the turbulence offlow of fluids thereacross.

The fin member 32 illustrated in the righthand portion of Figure 4 ofthe drawing is in all material respects similar to the fin member 21just described except that in this instance the alternate fin portions33 and 34 are twisted in opposite directions. While I have illustratedthese modifications as embodying eight fin portions in each member,those skilled in the art will appreciate that a greater or lesser numbercan be employed without departing from the teachings of my invention. Inthese modifications, the greater number of spaces between fin portionsmakes possible a greater number of welded areas and a correspondingincrease in the cross-sectional area of the paths for the conducinglydecreased.

6 tion of heat between the tube and the fins. As noted above, the numberof welds employed with fins such as illustrated in Figures 1, 2 and 3may also be increased over the four welds per member heretoforedescribed.

In- Figures 5, 6 and '7 I have illustrated a construction modified intwo respects, either modification being useful without the other. Herethe tube 35 has a plurality of circumferential fin members 36 thereon.These fin members comprise fin portions 31 and hub or base portions 38,the fin portions being separated by aligned spaces or slots 39 so thatthe welding operation can be carried out in longitudinal directions.

Here the base portions 38 are not continuous, but slots 40 are providedbetwen the spaces 39. These preferably extend through the base portionsand radially outwardly as far as practical, for example, aboutthree-quarters of the way into the fin portions as shown. The slots havea dual function. First, they give the base or hub portions of the finmembers a certain amount of resilience and flexibility which solid hubportions would not have, thus enabling the tolerances in the diametersof the tube and hub portions to be slightly greater while insuringproper fit and making the assembly of the fin members on the tubesomewhat easier.

A second, and perhaps more important advantage of the slots is found inthe fact that they increase the length of the paths for the flow ofelectricity through the fin members between the electrodes 4| and 42,thus increasing the resistance to the passage of current through the finmembers themselves. This current, of course, is useless insofar asweldin the base portions to the tube is concerned, and has thedisadvantageous effect of merely heating the base portions withoutserving any useful purpose. With slots such as those illustrated, thelength of the path that must be traversed by the current issubstantially increased, thu the resistance is increased and the amountof current correspond- Insofar as the welding operation is concerned-theslots give the advantage that would be obtained by the use of separatefin portions, yet the members are integral and held together so thatthey may be readily handied and retained in position on the tube priorto and during the welding operation.

In some instances, it is desirable to provide tubes with longitudinal aswell as circumferential fins. The longitudinal fins not only increasethe effective heat transfer surface of the tube, but also have the veryimportant advantage of increasing the structural strength of the tubes.This is of great importance where tubes of considerable length aresubjected to relatively high temperatures. Under such circumstances,plain tubes or tubes provided merely with circumferential fins may sagfrom their own weight and the weight of the fluid within them.Longitudinally extendin fins greatly increase thev strength of the tubeand their ability to resist such deflection.

Tubes embodying my invention can readily be provided with suchlongitudinally extendin fins. This is accomplished by the methoddiagrammatically shown in Figure 5 wherein a pair of channel section finmembers 43 and 44 are diswelding current caused to flow simultaneouslyto weld the oppositely disposed channel members to the base portions bya series of welded areas, and to weld the base portions of the finmembers to the tube. The welds are indicated diagrammatically at 45 and46 in Figure 5, and as shown in Figure 6, extend throughoutsubstantially the entire length of the channels. The welded areas arepreferably proportioned with respect to the cross-sectional area of theflanges of the channel to give adequate paths for the fiow of heat inthe manner taught, for example, in my Patent No. 2,261,137, issuedNovember 4, 1941. It will be noted that the hub or base portions 38 ofthe members 35 are shown in the drawing as being somewhat longer thanthe base portion i6 previously described. This results in greaterspacing of the radial fins and larger welded areas for each fin member.The length of the hubs or base portions and, correspondingly, thespacing of the radial fin members, may be varied to suit differentrequirements.

Ordinarily only a single pair of oppositely disposed channel section finmembers will be welded along such a tube, the welds along the remainingpaths extendin longitudinally of the tube being mad merelybetween thebase portions of the fin members and the tube as at 4'! and ll inFigures 5 and 7. 'A highly advantageous construction results when theedges of the flanges of the channels are bent inwardly into contact witheach other as at 49 in Figure 7 and welded together, thus producing aclosed-in fin of the type described in greater detail in my applicationaforesaid. The bending and welding operations may also be carried out asdescribed in said application. This produces a structurally strong tubein which the longitudinally extending fins add to the strength of thetube, increase the effective heat transfer surface of the tube, and inaddition, somewhat streamline the tube to reduce the resistance to fiowof fluid across the tube in directions parallel to the longitudinallyextending fins.

From the foregoing description of preferred form of my invention, itwill be seen that I have provided a heat exchanger element in whichtransversely extending fin members can be welded rapidly to the elementby means of welding operations carried out in longitudinal directions.By this means the rapidity and economy of the welding operations aregreatly increased as compared to methods wherein flanges arecircumferentia-lly welded to tubes, while the welded areas are such asto insure adequate paths for the flow of heat between the tubes and thefin members. The fin members themselves can be made rapidly andeconomically by stamping operations from relatively inexpensivematerials. The shape and size and arrangement of several fin portionscan be varied widely to suit different operating conditions, and ifdesired, the fin portions may be twisted, bent or otherwise formed toincrease the turbulence of flow of fiuid across the heated surface. Ifdesired, longitudinal fins may be welded to the tube simultaneously withthe welding operations for securing the circumferentially extending finsthereto, thus producing a structure having advantageous characteristicsfrom the standpoint of strength, heat transfer ability and fiowcharacteristics.

In the foregoing specification I have described various preferred formsof my invention. Further modifications and changes in my invention maybe made without departing from the spirit and scope thereof. Forexample, the specification and drawings describe and illustrate the finsas applied to the exterior of round tubes, the fins may be applied tosupporting surfaces of other shapes or configurations wherever thewelding operations can be carried out in directions transverse to thesurface of the fins. Other changes and modifications will doubtlessoccur to those skilled in the art. It is therefore to be understood thatmy patent is not limited to the preferred forms described herein or inany manher other than by the scope of the appended claims.

I claim:

1. A heat exchange element comprising a supporting surface and a seriesof transverse fin members united thereto, each transverse fin membercomprising a base portion lying along the supporting surface and aplurality of fin portions formed integrally with said base portion andprojecting away from said supporting surface, said fin portions beingspaced apart by spaces extending to the base portion, each fin memberhaving at least one such space. said fin members being arranged on saidsupporting surface with their spaces in substantial alignment to providean unobstructed path therethrough, a longitudinal fin member disposedwithin said path and having a base portion Joined to the base portionsof the transverse fin members. the base portions of the transverse finmembers being united to the supporting surface along said path.

2. A tube having a plurality of fin members secured thereto, each finmember comprising a base portion embracing the tube and a plurality ofspaced transverse fin portions extending therefrom and lying generallytransverse to the axis of the tube, the spaces between the transversefin portions of the several fin members being substantially inalignment, a longitudinal member disposed along the path formed by saidaligned spaces, the base portions of adjacent fin members beingsubstantially in contact with each other, and said longitudinal memberbeing secured to said base portions and said base portions being securedto the tube by welded areas extending along said path.

3. A tube having a plurality of fin members secured thereto, each finmember comprising a base portion embracing the tube and a plurality ofspaced transverse fin portions extending therefrom and lying generallytransverse to the axis of the tube, the spaces between the transversefin portions of the several fin members being substantially inalignment, a longitudinal member having a base portion and twolongitudinally extending flanges, said member being disposed along thepath formed by said aligned spaces, the base portions of adjacent finmembers being substantially in contact with each other, and saidlongitudinal member being secured to said base portions and said baseportions being secured to the tube by welded areas extending along saidpath.

4. A tube having a plurality of fin members secured thereto, each finmember comprising a base portion embracing the tube and a plurality ofspaced fin portions extending therefrom and lying in planes generallytransverse to the axis of the tube, the spaces between the fin portionsof the several fin members being substantially in alignment, a closed,hollow longitudinal member extending along the path formed by saidaligned spaces, the base portions of adjacent fin members beingsubstantially in contact with each 9 other, and said longitudinal memberbeing socured to said base portions and said base portions being securedto the tube by welded areas extending along said path. 1

5. A heat exchange element comprising a metallic tube; a plurality oftransversely disposed metallic fln members projecting radially from thesurface of said tube and formed with one or more alined radiallyextending slots; and one or more longitudinal fins extending axially ofthe tubes,

and disposed each in one oi said slots.

JOHN W. BROWN, JR.

REFERENCES CITED The following references are of record in the 15 tileof this patent:

UNITED STATES PATENTS Number Name Date 2,261,136 Brown, Jr. Nov. 4, 19412,261,137 Brown, Jr. Nov, 4, 1941 OTHER REFERENCES The Welding Journal,Feb. 1940. Dane 96.

20 (Copy in Div. 60.)

